Applications that access a relational database reference objects in the database (tables, columns, etc.) by name. This creates a close coupling between applications and the database objects. This close coupling causes complications when upgrading either the database or the application. This situation is exacerbated when multiple applications may reference the same objects and those applications may themselves be upgraded at different times at an installed site.
A traditional solution to the aforementioned problem is to make use of the "view" construct typically provided by relational databases. The use of database view, however, is problematic due to the well-known deficiencies of updating views and because views often incorporate non-standard SQL syntax in their definitions. Being able to run on relational databases from different vendors is a desirable capability.